JP5258184B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for transferring a transfer image line developed by writing a scanning line (hereinafter referred to as a latent image line) of an electrostatic image on an image carrier onto a recording material using an intermediate transfer body, and more particularly to a recording material. The present invention relates to the interval control of transferred transfer image lines (scanning lines).

  2. Description of the Related Art Electrophotographic image forming apparatuses are widely used in which latent image lines in the main scanning direction are successively written on a photosensitive drum that rotates in the sub-scanning direction, developed with toner, and the developed toner images are transferred to various recording materials. ing. A tandem type image forming apparatus in which a plurality of photosensitive drums are arranged along a belt member and individual color toner images formed on the respective photosensitive drums are superimposed to form a full color image has been put into practical use. The belt member includes a recording material conveying belt that conveys the recording material and contacts the photosensitive drum, and an intermediate transfer belt that secondarily transfers the toner image primarily transferred from the photosensitive drum to the recording material at the secondary transfer position. is there.

  In an electrophotographic image forming apparatus, an image is scanned by scanning a laser beam light that has been modulated according to pixel gradation, or by intermittently emitting a line image exposure head in which light emitting elements are arranged for each pixel. Write latent image lines on the carrier. A large number of transfer image lines in which the latent image lines written in the main scanning direction are developed with toner are arranged in the sub-scanning direction on the surface of the image carrier to form a transfer image (toner image). Therefore, when the interval (sub-scanning direction pitch) of the latent image lines written on the image carrier varies, stripe-like and band-like density unevenness is formed in the transferred image.

  Patent Document 1 discloses a tandem type image forming apparatus in which cyan, magenta, yellow, and black image forming stations are arranged along a recording material conveyance belt. The photosensitive drum of each image forming station is pressed against the recording material conveyance belt, and the recording material conveyance belt is driven to rotate the photosensitive drum by friction transmission.

  Then, by detecting the amount of displacement of the peripheral surface of the photosensitive drum and adjusting the optical writing timing or the writing position in the moving direction of the photosensitive drum, the interval between the latent image lines in one rotation cycle due to the eccentricity of the photosensitive drum is adjusted. The variation is offset.

  Patent Document 2 discloses an image forming apparatus in which an intermediate transfer belt and a photosensitive drum are driven by separate pulse motors. Here, the writing interval of the latent image lines on the photosensitive drum is changed in a predictive manner corresponding to the region where the speed of the intermediate transfer belt fluctuates, and as a result, the transfer image lines at equal intervals are primarily transferred onto the intermediate transfer belt. I try to do it.

Japanese Patent Laid-Open No. 10-246995 JP 2002-278204 A

  The driving method disclosed in Patent Document 2 requires separate and expensive driving systems for the intermediate transfer belt and the photosensitive drum, and therefore, if a plurality of image forming stations are arranged along the intermediate transfer belt, the component cost becomes excessive. The mechanism structure of the image forming station becomes complicated, and the size of the image forming apparatus increases.

  The control method disclosed in Patent Document 1 can solve the variation in the interval between the latent image lines due to the eccentricity of the photosensitive drum, but the cause of the fluctuation in the surface speed of the photosensitive drum is not limited to the eccentricity of the photosensitive drum. Therefore, if the surface speed of the photosensitive drum fluctuates for reasons other than the eccentricity of the photosensitive drum, the interval of the latent image lines written at a fixed position and time interval varies depending on the amount of fluctuation of the surface speed, and the transferred image has fringes. And band-like density unevenness are formed.

  In the driving method disclosed in Patent Document 1, the photosensitive drum is driven and rotated by the recording material conveyance belt, so that the rotational speed of the photosensitive drum varies at the same time as the recording material conveyance belt varies in speed. At this time, if a latent image line having a fixed period is written at a fixed writing position on the photosensitive drum, the interval between the latent image lines varies corresponding to the speed fluctuation of the photosensitive drum.

  Therefore, with reference to Patent Document 1, a proposal has been made to detect the surface speed (or rotational speed) of each photosensitive drum and adjust each writing position (or writing time) every moment. However, if the surface speed (or rotational speed) detecting means is provided in each of the four photosensitive drums in total, and the writing position (or writing time) adjustment circuit is provided in each of the four exposure apparatuses in total, the component cost is reduced. Get higher. When the number of parts around the photosensitive drum increases, it is difficult to reduce the size of the image forming apparatus and improve the maintainability.

  An object of the present invention is to provide an image forming apparatus that can reduce density unevenness of a transfer image due to reasons other than the eccentricity of a photosensitive drum. An object of the present invention is to provide an image forming apparatus capable of reducing density unevenness of a transfer image line with a set of detection means and an adjustment circuit even when a plurality of photosensitive drums are arranged along a recording material conveyance belt or an intermediate transfer belt. Yes.

  By the way, when the transfer image line primarily transferred to the intermediate transfer belt is secondarily transferred to the recording material at the secondary transfer position, the density of the transfer image line on the recording material is adjusted even if the intervals of the transfer image lines on the intermediate transfer belt are uniform. Unevenness may occur. When there is a relative speed fluctuation between the recording material conveyance speed and the intermediate transfer belt circulation speed at the secondary transfer position, the distance between the transfer image lines on the intermediate transfer belt and the distance between the transfer image lines on the recording material. This is because does not match.

  Another invention having the above-mentioned purpose in common cancels the relative speed fluctuation between the recording material conveyance speed at the secondary transfer position and the circulation speed of the intermediate transfer belt, and the final transfer image line on the recording material The purpose is to align the intervals.

The image forming apparatus of the present invention includes a plurality of image forming units each including a photosensitive member and an exposure unit that exposes the photosensitive member in which elements for each pixel are arranged in a rotation axis direction of the photosensitive member, and the plurality of image forming units. The images formed in the sections are sequentially superimposed and transferred primarily, and an intermediate transfer member that rotates the respective photosensitive members by rotating while contacting the respective photosensitive members, and a rotating unit that rotates the intermediate transfer member A transfer roller that collectively transfers a primary transferred image on the intermediate transfer body onto a recording material at a secondary transfer portion, and a recording material by driving the transfer roller at the secondary transfer portion. in the image forming apparatus having a transfer roller driving means for conveying a detecting means for detecting the rotational speed of the intermediate transfer member, based on an output of said detecting means, by said exposing means in the rotation direction of the photosensitive member Based on the output of the detection means, exposure control means for performing exposure control for adjusting the exposure time interval of the exposure means in common and simultaneously in the plurality of image forming units so that the distance between the dots is constant, And a speed control means for controlling the driving speed of the transfer roller driving means so that the conveyance speed of the recording material follows the rotational speed of the intermediate transfer member.

An image forming apparatus according to another aspect of the invention includes a plurality of image forming units each including a photoconductor and an exposure unit that exposes the photoconductor with a laser beam, and an image formed by the plurality of image forming units is sequentially overlapped to perform primary transfer. In addition, the intermediate transfer member that rotates the respective photosensitive members by rotating while contacting the respective photosensitive members, a rotating unit that rotates the intermediate transfer member, and the primary transfer on the intermediate transfer member. An image having a transfer roller that collectively transfers images to a recording material at a secondary transfer unit, and a transfer roller driving unit that conveys the recording material by driving the transfer roller at the secondary transfer unit. In the forming apparatus, based on the output of the detection means for detecting the rotation speed of the intermediate transfer member and the output of the detection means, the distance between dots by the exposure means in the rotation direction of the photosensitive member is made constant. An exposure control means for performing exposure control for adjusting the exposure position in the rotation direction of the photosensitive member in common and simultaneously in the plurality of image forming units, and an instantaneous rotation speed of the intermediate transfer body based on the output of the detection means And a speed control means for controlling the driving speed of the transfer roller driving means so as to follow the conveying speed of the recording material.

  In the image forming apparatus of the present invention, transfer image lines in the main scanning direction are arranged in the sub-scanning direction on the surface of the image carrier, and finally a transfer image to be transferred to the recording material is formed. In order to reduce the variation in the interval between the transfer image lines on the recording material, the variation in the interval between the transfer image lines in the sub-scanning direction on the surface of the image carrier is reduced.

The electrostatic image line writing position (writing timing or writing position with respect to the image carrier) on the moving surface of the image carrier is adjusted in accordance with the speed variation of the intermediate transfer member . Since the image carrier is driven by the intermediate transfer member , as a result, the writing position of the electrostatic image line is adjusted according to the speed fluctuation of the surface of the image carrier. If the moving speed of the surface of the image carrier is high, adjust the direction to reduce the interval between the electrostatic image lines. If the moving speed of the surface of the image carrier is low, the time interval for forming the electrostatic image lines Adjust the direction to increase.

However, instead of directly detecting the moving speed of the surface of the image bearing member, the moving speed of the intermediate transfer member that moves the image bearing member is detected, and the electrostatic transfer amount is adjusted according to the variation amount of the moving speed of the intermediate transferring member. Adjust the image line writing position.

Therefore, all the image carriers that follow the intermediate transfer member can be adjusted simultaneously with a common adjustment amount, and even when there are a plurality of image carriers, the speed is detected for each image carrier and the adjustment amount for each image carrier is adjusted. There is no need to define. The speed information necessary for adjusting the writing position is acquired at a position away from the image carrier where a large number of devices and parts are arranged in the vicinity, and density unevenness of the transferred image due to reasons other than the eccentricity of the image carrier is reduced. be able to. It is possible to cancel variations in the surface speed of the image carrier due to reasons other than the eccentricity of the image carrier, and to reduce variations in the distance between transfer image lines in the state where the image is finally transferred to the recording material.

In addition, by performing drive control of the recording material conveying means that cancels out the relative speed difference between the intermediate transfer member and the recording material in the secondary transfer unit , the interval between the transfer image lines that are primarily transferred to the intermediate transfer member is maintained as it is. Deliver to recording material. Accordingly, the transfer image lines that are primarily transferred to the intermediate transfer member at equal intervals are secondarily transferred to the recording material at equal intervals. A transfer image that has been primarily transferred to the intermediate transfer member without density unevenness (a large number of transfer image lines that have been primarily transferred without unevenness in spacing) is secondarily transferred to the recording material without density unevenness.

  Hereinafter, an image forming apparatus 100 according to an embodiment of the present invention will be described in detail with reference to the drawings. The image forming apparatus of the present invention is not limited to the limited configuration of the embodiments described below. As long as the variation in the distance between the transfer image lines in the state of being finally transferred to the recording material is reduced to reduce the density unevenness and the color tone unevenness of the transfer image, a part or all of the configuration of each embodiment is substituted. It is also possible to realize another embodiment that is replaced by a typical configuration.

  In the present embodiment, a tandem type image forming apparatus in which four photosensitive drums 11 a to 11 d are arranged along the intermediate transfer belt 31 will be described. However, the image forming apparatus of the present invention may be an image forming apparatus in which a plurality of photosensitive drums are arranged along the recording material conveyance belt, and the number of photosensitive drums may be other than four.

  The image forming apparatus 100 according to the present embodiment can be realized as an image forming apparatus for various uses such as a printer, various printing machines, a copier, a FAX, and a multifunction machine.

  Note that the configuration of the image forming apparatus disclosed in Patent Documents 1 and 2, the detailed structure and control of each mounted apparatus, the adjustment method of the writing position, etc., are omitted in detail to avoid repeated complications. Detailed explanations are also omitted.

<First Embodiment>
FIG. 1 is a cross-sectional view showing the overall configuration of the image forming apparatus according to the first embodiment, and FIG. 2 is an explanatory diagram of a photosensitive drum driving mechanism. FIG. 3 is an explanatory diagram of the latent image line on the photosensitive drum having no speed variation, FIG. 4 is an explanatory diagram of the speed variation of the photosensitive drum, and FIG. 5 is an explanatory diagram of the latent image line on the photosensitive drum having the speed variation.

  As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment is a tandem type electrophotographic color copying machine that forms a full-color transfer image by superimposing four separated color toner images on an intermediate transfer belt 31. is there. The intermediate transfer belt 31 driven by the driving roller 32 presses the four photosensitive drums 11a to 11d and rotates them by friction transmission. A speed change of the intermediate transfer belt 31 is detected by a rotary encoder (37: FIG. 6) provided on the rotation shaft of the drive roller 32. Then, the writing positions of the latent image lines on the four photosensitive drums 11a to 11d are simultaneously adjusted by using one adjustment amount corresponding to the speed fluctuation amount.

  The image forming apparatus 100 includes an image reading unit 1R that reads an image from a document, and an image output unit 1P that forms an image on a recording material and outputs the read image and externally input image data. The image reading unit 1R optically reads an image on the lower surface of the document placed on the glass plate surface, converts it into an electrical signal, and transmits it to the image output unit 1P. In the image output unit 1P, a toner image forming unit 10, an intermediate transfer unit 30, a recording material feeding unit 20, a fixing unit 40, a belt cleaning unit 50, and a control unit 80 are arranged.

  The toner image forming unit 10 includes yellow (Y), cyan (C), magenta (M), and black (K) image forming stations 10d, 10c, 10b, and 10a from the upstream side along the intermediate transfer belt 31. . The image forming stations 10d, 10c, 10b, and 10a are configured in common by changing only the separation color toners filled in the developing devices 14d, 14c, 14b, and 14a. Therefore, in the following, the image forming station 10a at the most downstream side will be described, and description of the image forming stations 10b to 10d that are similarly described by replacing the subscript a with b to d will be omitted.

  A primary charging device 12a, an exposure device 13a, a developing device 14a, a primary transfer roller 35a, and a cleaning device 15a are disposed around the photosensitive drum 11a that rotates in the direction of the arrow and moves the surface in the sub-scanning direction. The primary charging device 12a uniformly charges the surface of the photosensitive drum 11a. The exposure device 13a is composed of an LED array in which LED elements are arranged for each pixel in the main scanning direction, and the light emission amount (number of times of light emission) corresponding to the black density gradation of the pixels is set in the LED elements to thereby expose the surface of the photosensitive drum 11a. Write a black latent image line in

  The developing device 14a develops the latent image line into a transfer image line by supplying charged black toner to the surface of the photosensitive drum 11a and electrostatically adhering it to the latent image line. On the surface of the photosensitive drum 11a, transfer image lines are arranged in the sub-scanning line direction to form a black transfer image (toner image).

  The primary transfer roller 35a is applied with a primary transfer bias voltage having a polarity opposite to the charging polarity of the toner, and electrostatically moves the transfer image line on the surface of the photosensitive drum 11a to the intermediate transfer belt 31 side for primary transfer. The cleaning device 15a scrapes off the primary transfer residual toner remaining on the surface of the photosensitive drum 11a with a rubber blade to prepare for the next uniform charge to primary transfer.

  The intermediate transfer unit 30 forms a full-color transfer image on the intermediate transfer belt 31 by superimposing the respective separation color transfer images respectively formed by the image forming stations 10 d, 10 c, 10 b, and 10 a. The intermediate transfer belt 31 is wound around a driving roller 32, a driven roller 33, a secondary transfer counter roller 34, and primary transfer rollers 35a, 35b, 35c, and 35d. As the intermediate transfer belt 31, for example, PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride), or the like is used.

  The drive roller 32 (drive means) is connected to a drive motor (38: FIG. 2) and transmits drive to the intermediate transfer belt 31. The driving roller 32 is coated with rubber (urethane or chloroprene) having a thickness of several millimeters on the surface of the metal roller to prevent slippage with the belt.

  The driven roller 33 rotates following the circulation of the intermediate transfer belt 31 and is biased by a spring (not shown) to apply an appropriate tension to the intermediate transfer belt 31. The secondary transfer counter roller 34 presses the intermediate transfer belt 31 outward to press the secondary transfer roller 36, and forms a secondary transfer nip Te for secondary transfer of the transfer image onto the recording material P.

  A primary transfer plane A is formed on the intermediate transfer belt 31 between the driving roller 32 and the driven roller 33. The primary transfer rollers 35a, 35b, 35c, and 35d press the intermediate transfer belt 31 to the photosensitive drums 11a, 11b, 11c, and 11d to form primary transfer nips Ta, Tb, Tc, and Td on the primary transfer plane A.

  The recording material feeding unit 20 takes out the recording materials P stored in the cassette 21 one by one and feeds them to the secondary transfer nip Te. A plurality of cassettes 21 are arranged for each size of the recording material P, and the recording material P can be supplied also from a manual feed tray (not shown). The pickup roller 22 separates the recording material P from the cassette 21 one by one and transfers it to the paper feed roller pair 23. The paper feed roller pair 23 conveys the recording material P along the paper feed path 24 and delivers it to the registration rollers 25a and 25b. The registration rollers 25a and 25b send the recording material P to the secondary transfer nip Te in synchronization with the full-color transfer image formed on the intermediate transfer belt 31.

  In the fixing unit 40, a fixing roller 41a and a pressure roller 41b are arranged inside heat insulating covers 46 and 47 for confining heat inside. The fixing roller 41a and the pressure roller 41b are each incorporated with a halogen heater as a heat source and are pressed against each other at a predetermined pressure to form a fixing nip that conveys the recording material P while being heated and pressurized. The guide 43 guides the recording material P on which the transferred image is secondarily transferred to the fixing nip.

  The belt cleaning unit 50 cleans the transfer image transfer surface of the intermediate transfer belt 31 on the downstream side of the secondary transfer nip Te to prepare for the next primary transfer. The belt cleaning unit 50 includes a cleaning blade 51 for removing toner on the intermediate transfer belt 31 and a waste toner box 52 for storing waste toner.

  The control unit 80 is a control device that includes a computer control circuit, various fixed control circuits, a communication circuit, a driver circuit, and the like, and controls the image reading unit 1R and the mechanisms of the image output unit 1P to perform an image forming process. Control. The control unit 80 includes an image processing unit that transfers an image signal from the image reading unit 1R to the exposure devices 13a, 13b, 13c, and 13d.

  When an image formation start signal is issued from the control unit 80, the toner image forming unit 10 causes the transfer image formed on the photosensitive drum 11d located on the most upstream side to be transferred to the intermediate transfer belt 31 in the primary transfer nip Td by the process described above. Primary transcription. The first transferred image is conveyed to the next primary transfer nip Tc.

  In the photosensitive drum 11c, a transfer image is formed by delaying the transfer image between the photosensitive drums 11d and Tc, and is superimposed on the yellow transfer image primarily transferred in the primary transfer nip Td. A cyan transfer image is primarily transferred at the primary transfer nip Tc.

  The same process is repeated at the primary transfer nip Tb of the photosensitive drum 11b and the primary transfer nip Ta of the photosensitive drum 11a, and finally, the four color transfer images are superimposed on the intermediate transfer belt 31 and primarily transferred.

  On the other hand, in response to the image formation start signal, the recording material feeding unit 20 starts the paper feeding operation from the cassette 21 selected according to the selected paper size or the like. For example, the recording material P is sent out from the cassette 21 one by one by the pickup roller 22. Then, the transfer material P is conveyed by the paper feed roller pair 23 and abuts against the nip portions of the registration rollers 25a and 25b in the stopped state.

  Thereafter, the registration rollers 25a and 25b start to rotate in accordance with the timing at which the toner image forming unit 10 starts forming the transfer image. The rotation timing is set so that the transfer image primarily transferred from the toner image forming unit 10 onto the intermediate transfer belt 31 coincides with the recording material P in the secondary transfer nip Te.

  Thereafter, when the recording material P enters the secondary transfer nip Te and contacts the intermediate transfer belt 31, a secondary transfer bias voltage is applied to the secondary transfer roller 36 in accordance with the passing timing of the recording material P. As a result, the four color transfer images formed on the intermediate transfer belt 31 are transferred onto the surface of the recording material P.

  Thereafter, the recording material P is accurately guided to the fixing nip of the fixing roller 41 a and the pressure roller 41 b by the conveyance guide 43. Then, the transfer image is fixed on the surface of the recording material P by receiving heat and pressure at the fixing nip. The recording material P on which the transfer image has been fixed by the fixing unit 40 is transferred from the inner discharge roller 44 to the outer discharge roller 45, and discharged and stacked on the discharge tray 48.

  As shown in FIG. 2, the surface of the photosensitive drum 11a is in pressure contact with the intermediate transfer belt 31 by the urging of the primary transfer roller 35a. The primary transfer roller 35a is biased by springs at both shaft ends (not shown), and the biasing force is 35 N (3.5 kgf).

  A drive roller 32 that drives the intermediate transfer belt 31 is connected to a drive motor 38. When the drive motor 38 rotates, the drive roller 32 rotates, and the intermediate transfer belt 31 stretched around the drive roller 32 circulates. Since the photosensitive drum 11a is in pressure contact with the intermediate transfer belt 31, the photosensitive drum 11a is driven to rotate in the direction of the arrow by friction transmission. The photosensitive drums 11b, 11c, and 11d are also rotated by the intermediate transfer belt 31 with the same mechanism configuration as that of the photosensitive drum 11a.

  As shown in FIG. 3, it is assumed that the exposure device 13a (LED array) writes latent image lines eight times at equal time intervals while the photosensitive drum 11a rotates once in the direction of the arrow. Here, in order to help the understanding of the explanation, the exposure is made 8 times per round, but in actuality, when the resolution in the sub-scanning direction is 600 DPI with the photosensitive drum 11a of Φ30, the exposure is about 2226 times per round. . Since the peripheral length of the photosensitive drum 11a is 64247.780 (μm) and 600 DPI is 42.333 (μm), 64247.780 ÷ 42.333 = about 2226 in one rotation of the photosensitive drum 11a.

  When there is no rotation unevenness in the photosensitive drum 11a, the photosensitive drum 11a rotates at a uniform angular velocity, so that the exposure device 13a writes latent image lines at a uniform angle with respect to the surface of the photosensitive drum 11a, that is, every 45 degrees. Thereby, latent image lines are formed at the eight writing positions K1 to K8.

  However, as shown in FIG. 4, when the photosensitive drum 11 has rotation unevenness and the surface speed fluctuates, the exposure device 13a exposes the surface of the photosensitive drum 11a at a position corresponding to the speed fluctuation. . As a result, as shown in FIG. 5, the writing positions H1 to H8 when there is rotational unevenness do not necessarily match the writing positions K1 to K8 when there is no rotational unevenness. At the writing positions H3 to H5 where the surface speed is high, the latent image line writing interval is large, and at the writing positions H6 to H2 where the surface speed is low, the latent image line writing interval is small.

  In other words, when there is rotation unevenness as shown in FIG. 4, the amount of movement of the surface of the photosensitive drum 11a per unit time changes. When there is no rotation unevenness in the photosensitive drum 11a, the amount of movement of the surface of the photosensitive drum 11a is always constant as indicated by a dotted line in FIG. However, when the photosensitive drum 11a has rotation unevenness, the amount of movement of the surface of the photosensitive drum 11a per unit time varies as shown by the solid line. At the writing positions H1 and H2, the rotational speed is slow, so the amount of movement is smaller than the dotted line without rotation unevenness, and then the rotational speed gradually increases. At the writing positions H3 to H5, the amount of movement is larger than the dotted line without rotational unevenness. Many. After that, since the rotation speed becomes slower, the movement amount is smaller at the writing positions H7 and H8 than the dotted line. If the intervals between the latent image lines are not uniform due to the rotation unevenness, distortion of the transferred image and density unevenness in the sub-scanning direction are caused.

<Latent image line writing timing control>
FIG. 6 is an explanatory diagram of the control of the exposure apparatus and the secondary transfer roller, and FIG. 7 is an explanatory diagram of the control result. In FIG. 7, (a) is the rotation unevenness of the drive roller 32, (b) is the circulation speed unevenness of the intermediate transfer belt 31, and (c) is the rotation unevenness of the photosensitive drum 11a. (D) shows variations in the transfer image line spacing when the control of the first embodiment is not performed, and (e) shows variations in the transfer image line spacing when the control of the first embodiment is performed. In the first embodiment, the rotation unevenness of the driving roller 32 is detected and the exposure timing of the exposure devices 13a, 13b, 13c, and 13d and the rotation speed of the secondary transfer roller 36 are controlled.

  As shown in FIG. 6, the transfer belt 31 is transported and driven by a drive roller 32, and the photosensitive drums 11 a, 11 b, 11 c, and 11 d are frictionally driven by being pressed against the transfer belt 31. Rotating driven. The drive roller 32 is connected to a rotary encoder 37 for detecting uneven rotation of the drive roller.

  FIG. 7A shows the displacement of the output of the encoder 37 indicating the angular velocity when the drive roller 32 rotates. The dotted line shown in FIG. 7A is the angular velocity of the drive roller 32 when there is no rotation unevenness, and is always constant, but in reality there is rotation unevenness, so the angular velocity varies as shown by the solid line.

  As shown in FIG. 7B, the conveyance speed of the intermediate transfer belt 31 driven by the driving roller 32 also varies according to the variation in the angular velocity of the driving roller 32. Then, the photosensitive drums 11a, 11b, 11c, and 11d driven by the intermediate transfer belt 31 also vary in angular velocity of rotation as shown in FIG.

  The fluctuation in the conveyance speed of the intermediate transfer belt 31 shown in FIG. 7B and the fluctuation in the angular speed of the photosensitive drum 11a shown in FIG. 7C are the angular speed of the driving roller 32 shown in FIG. It is in phase with the fluctuation.

  As shown in FIG. 7C, when the exposure device 13a exposes the photosensitive drum 11a whose rotational speed fluctuates at equal time intervals, latent image lines are written on the photosensitive drum 11a at different intervals. End up. As a result, when the transfer image line obtained by developing the latent image line is primarily transferred to the intermediate transfer belt 31, the interval between the transfer image lines on the intermediate transfer belt 31 varies as shown in FIG. Although the transfer image lines are intended to be formed at equal intervals, in reality, due to the rotation unevenness of the drive roller 32, the transfer image line interval becomes rough when the speed is high, and the transfer image line interval becomes low when the speed is low. It becomes dense.

Therefore, the output of the rotary encoder 37 is input to the control unit (write control means) 80 to count the output pulses, and exposure is performed by the exposure device 13a every predetermined pulse count. Therefore, when the moving speed of the surface of the photosensitive drum 11a is high, the frequency of the pulse output increases and exposure is performed at short time intervals. Then, when the moving speed of the surface of the photosensitive drum 11a is low, the frequency of the pulse output decreases and exposure is performed at a long time interval.

  As a result, fluctuations in the moving speed of the surface of the photosensitive drum 11a in conjunction with fluctuations in the speed of the intermediate transfer belt 31 are canceled out, and latent image lines are written at equal intervals on the surface of the photosensitive drum 11a. Even if the drive roller 32 has rotation irregularities, latent image lines can be written at equal intervals on the surface of the photosensitive drum 11a. By developing the latent image lines at equal intervals into transfer image lines and performing primary transfer onto the intermediate transfer belt 31, the transfer image lines at equal intervals are arranged on the intermediate transfer belt 31 as shown in FIG. it can.

  The photosensitive drums 11b, 11c, and 11d are also controlled using the same control amount at the same time, and variations in the interval between the latent image lines due to the speed fluctuation of the intermediate transfer belt 31 are eliminated.

  However, when the circulation speed of the intermediate transfer belt 31 is uneven, when the recording material P is conveyed at a constant speed by the secondary transfer roller 36, the transfer image lines arranged at equal intervals on the intermediate transfer belt 31 are recorded. Secondary transfer to P at equal intervals is not possible.

  Accordingly, the rotational speed of the motor 601 that drives the secondary transfer roller 36 is intentionally varied in accordance with the rotational unevenness of the driving roller 32, and the transfer speed of the transfer material P follows the momentary circulation speed of the intermediate transfer belt 32. I am letting. The pulse output of the rotary encoder 37 is input to the motor control unit 602, and the rotational speed of the motor 601 is controlled in proportion to the frequency of the pulse signal.

  Specifically, the motor 601 is a pulse motor, and the pulse output of the rotary encoder 37 is used as a clock pulse to be input to the pulse motor driver that is the motor control unit 602. The drive roller 32, the secondary transfer roller 36, and the like are designed so that the movement amount of the intermediate transfer belt 32 for one pitch of the clock pulse matches the surface movement amount of the secondary transfer roller 36 for one pitch of the clock pulse. .

  The motor control unit 602 generates a drive signal for the motor 601 based on the pulse signal from the rotary encoder 37. As a result, even if there is uneven circulation speed of the intermediate transfer belt 31 due to uneven rotation of the drive roller 32, the transfer image lines are secondarily transferred onto the recording material P without changing the interval on the intermediate transfer belt 31, Density unevenness can be eliminated.

  The image forming apparatus 100 according to the first embodiment employs a driven drive system in which the photosensitive drums 11a, 11b, 11c, and 11d are in pressure contact with the intermediate transfer belt 32 and driven to rotate. Accordingly, even with simple control using an inexpensive drive source with relatively large rotation unevenness, the circulation speed of the intermediate transfer belt 31 and the surface speed of the photosensitive drums 11a, 11b, 11c, and 11d are accurately matched to each other. Misalignment can also be prevented. Then, the exposure timing to the photosensitive drums 11a, 11b, 11c, and 11d and the conveyance speed of the recording material P are determined according to the output of the rotary encoder 37 that detects the rotation unevenness of the driving roller 32 of the intermediate transfer belt 31. . As a result, the color unevenness on the recording material P is reduced, and the image forming apparatus 100 with high image quality is provided.

  In the first embodiment, the rotary encoder is used as means for detecting the rotation unevenness of the drive roller 32. However, a uniform clock pattern may be formed on the intermediate transfer belt 31, and the clock pattern may be read by an optical sensor or the like. . By generating a pulse signal having a frequency proportional to the circulation speed of the intermediate transfer belt 31 and applying the same control as in the first embodiment, the same effect can be obtained that cancels out the speed fluctuation of the intermediate transfer belt 31.

Second Embodiment
FIG. 8 is an explanatory diagram of the control according to the circumferential displacement of the driving roller in the second embodiment. The second embodiment is configured in the same manner as the first embodiment except that the rotary encoder 37 in the first embodiment is replaced with a displacement measuring device 37B. Therefore, in FIG. 8, the same reference numerals are given to the same components as those in FIG. 1 and FIG.

  As shown in FIG. 8, in the second embodiment, the displacement of the driving roller 32 is detected using a displacement measuring device 37B. If the rotation axis of the drive roller 32 is eccentric, the distance to the center of rotation varies on the circumference of the drive roller 32 and the intermediate transfer belt 31 varies in speed. The change in the speed of the intermediate transfer belt 31 changes the rotation speed of the photosensitive drum 11a to vary the interval between the latent image lines.

  The displacement measuring device 37B outputs a pulse signal having a frequency proportional to the distance to the intermediate transfer belt 31. As in the first embodiment, the controller 80 counts the output pulses of the displacement measuring device 37B, and writes a latent image line on the surface of the photosensitive drum 11a by the exposure device 13a at every predetermined pulse count. By such simple control, as in the first embodiment, when the moving speed of the surface of the photosensitive drum 11a is high, the frequency of the pulse output increases and exposure is performed at short time intervals. Variations in the moving speed of the surface of the photosensitive drum 11a in conjunction with variations in the speed of the intermediate transfer belt 31 are canceled out, and latent image lines are written at equal intervals on the surface of the photosensitive drum 11a.

  Further, the rotational speed control of the motor 601 through the motor control unit 602 is also controlled in the same manner as in the first embodiment, and the transfer image line is secondarily transferred onto the recording material P without changing the interval on the intermediate transfer belt 31.

<Third Embodiment>
FIG. 9 is an explanatory diagram of exposure timing control of the exposure apparatus according to the third embodiment. The third embodiment is configured in the same manner as the first embodiment except that the exposure apparatus 13a and the like in the first embodiment are replaced with an exposure apparatus 13e and the like. Therefore, in FIG. 8, the same reference numerals are given to the same components as those in FIG. 1 and FIG.

  As shown in FIG. 9, the exposure device 13e scans the laser beam emitted from the light source 701 with a polygon mirror 702, irradiates the photosensitive drum 11a via the mirror 703, and writes a latent image line. The laser beam is pulse-modulated in response to pixel density changes along the main scanning line.

  The mirror 703 is supported by the rotary shaft 704 so as to be angularly displaceable, and is angularly displaced by the actuator 705. Therefore, by controlling the actuator 705 to displace the optical path of the polygon mirror scanning system, the writing position of the latent image line on the surface of the photosensitive drum 11a can be adjusted.

<Fourth embodiment>
In the fourth embodiment, the control of the first embodiment and the control of the second embodiment are performed simultaneously to adjust the latent image line writing position on the surface of the photosensitive drum 11 a and the rotation speed of the secondary transfer roller 36.

  That is, a synthesis circuit for inputting the output pulse of the rotary encoder 37 shown in FIG. 6 and the output pulse of the displacement measuring device 37B shown in FIG. 8 and outputting a clock pulse corresponding to the circulation speed of the secondary transfer belt 31 is added. To do. The synthesis circuit compares both output pulses and generates a clock pulse that rises and falls at an intermediate position between the two output pulses. By inputting the output pulse of the synthesis circuit to the control unit 80 and the motor control unit 602, the speed fluctuation of the secondary transfer belt 31 caused by both the rotation unevenness and the eccentricity of the drive roller 32 is offset.

<Correspondence with Invention>
The image forming apparatus 100 includes a rotating photosensitive drum 11, an exposure device 13 that forms an electrostatic image along the rotation axis direction of the photosensitive drum 11, and a developing device 14 that develops the electrostatic image to form a toner image. The intermediate transfer belt 31 on which the toner image on the photosensitive drum 11 is primarily transferred, the drive roller 32 that rotates the intermediate transfer belt 31, and the intermediate transfer belt 31. And a secondary transfer roller 36 for secondary transfer of the toner image to the recording material P at the secondary transfer portion. A rotary encoder 37 that detects the rotation speed of the intermediate transfer belt 31 is provided. Based on the detection result, the interval time during which the exposure device 13 forms an electrostatic image and the movement of the recording material P in the secondary transfer portion. Control the speed.

  In the image forming apparatus 100, a plurality of photosensitive drums 11 are arranged in pressure contact with the intermediate transfer belt 31, and the electrostatic image writing positions on the plurality of photosensitive drums 11 are simultaneously adjusted by a common adjustment amount based on the detection result. Is done.

  The image forming apparatus 100 includes a photosensitive drum 11 whose surface moves in the sub-scanning direction, an exposure device 13 that writes electrostatic image lines in the main scanning direction on the moving surface, and a developer on the written electrostatic image lines. And a developing device 14 that develops the transfer image line by moving the photosensitive drum 11, and the transfer image line is primary-transferred from the surface, and the transfer image is transferred to the recording material at the subsequent secondary transfer position. An intermediate transfer belt 31 for secondary transfer to P and a secondary transfer roller 36 for transporting the recording material P and passing it to the secondary transfer position are provided. A rotary encoder 37 that detects the moving speed of the intermediate transfer belt 31; a controller 80 that adjusts the writing interval of the electrostatic image lines on the photosensitive drum 11 by the exposure device 13 based on the output of the rotary encoder 37; A motor control unit 602 that adjusts the conveyance speed of the recording material P by the next transfer roller 36 based on the output of the rotary encoder 37;

  The rotary encoder 37 outputs a pulse signal corresponding to the rotational speed of the driving roller 32 that drives the intermediate transfer belt 31. The control unit 80 causes the exposure apparatus 13 to perform writing at each timing synchronized with the pulse signal.

  In the second embodiment, the displacement measuring device 37 </ b> B detects the displacement of the peripheral surface of the drive roller 32 that drives the intermediate transfer belt 31 by the detection unit.

  In the image forming apparatus 100, a plurality of photosensitive drums 11 are disposed in pressure contact with a common intermediate transfer belt 31, and the intermediate transfer belt 31 drives the plurality of photosensitive drums by friction. The moving speed of the intermediate transfer belt 31 is detected, and the interval between the electrostatic image lines written on the photosensitive drum is adjusted in accordance with the moving speed. The intervals in all the photosensitive drums 11 are adjusted simultaneously with a common adjustment amount.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus according to a first embodiment. It is explanatory drawing of the drive mechanism of a photosensitive drum. It is explanatory drawing of the latent image line in the photosensitive drum without a speed fluctuation | variation. It is explanatory drawing of the speed fluctuation | variation of a photosensitive drum. It is explanatory drawing of the latent image line in the photosensitive drum with a speed fluctuation | variation. It is explanatory drawing of control of an exposure apparatus and a secondary transfer roller. It is explanatory drawing of a control result. It is explanatory drawing of the control according to the surrounding surface displacement of the drive roller in 2nd Embodiment. It is explanatory drawing of exposure timing control of the exposure apparatus in 3rd Embodiment.

Explanation of symbols

10a, 10b, 10c, 10d Image forming stations 11a, 11b, 11c, 11d Image carrier (photosensitive drum)
13a, 13b, 13c, 13d Electrostatic image forming means, scanning line writing means (exposure apparatus)
14a, 14b, 14c, 14d Developing means (developing device)
31 Intermediate transfer member (intermediate transfer belt)
32 Drive means, drive roller member (drive roller)
34 Secondary transfer counter roller 36 Secondary transfer means, recording material conveying means (secondary transfer roller)
37, 37B detection means (rotary encoder, displacement measuring device)
40 fixing unit 80 control unit 100 image forming apparatus 601 motor 602 transport control means (motor control unit)

Claims (4)

A plurality of image forming units each including a photosensitive member and an exposure unit that exposes the photosensitive member in which elements for each pixel are arranged in a rotation axis direction of the photosensitive member;
The images formed by the plurality of image forming units are sequentially overlapped and primarily transferred, and an intermediate transfer member that rotates the respective photosensitive members by rotating while contacting the respective photosensitive members;
A rotating means for rotating the intermediate transfer member;
A transfer roller for performing a secondary transfer of the primary transferred image on the intermediate transfer body to a recording material in a batch at a secondary transfer portion;
An image forming apparatus having transfer roller driving means for conveying a recording material by driving the transfer roller in the secondary transfer section;
Detecting means for detecting the rotational speed of the intermediate transfer member;
Based on the output of the detection means, the exposure time interval of the exposure means is adjusted in common and simultaneously in the plurality of image forming units so that the inter-dot distance by the exposure means in the rotation direction of the photoconductor is constant. Exposure control means for performing exposure control;
And a speed control unit that controls the driving speed of the transfer roller driving unit so that the conveyance speed of the recording material follows the rotational speed of the intermediate transfer member based on the output of the detecting unit. An image forming apparatus. A plurality of image forming units each including a photoconductor and an exposure unit that exposes the photoconductor with a laser beam;
An intermediate transfer member that rotates the respective photoconductors by rotating while contacting the respective photoconductors, and sequentially transferring the images formed by the plurality of image forming units in order.
A rotating means for rotating the intermediate transfer member;
A transfer roller for performing a secondary transfer of the primary transferred image on the intermediate transfer body to a recording material in a batch at a secondary transfer portion;
An image forming apparatus having transfer roller driving means for conveying a recording material by driving the transfer roller in the secondary transfer section;
Detecting means for detecting the rotational speed of the intermediate transfer member;
Based on the output of the detection means, the exposure position in the rotation direction of the photoconductor in the rotation direction of the photoconductor is set to be common and simultaneously in the plurality of image forming units so that the distance between dots by the exposure means is constant. Exposure control means for performing exposure control to be adjusted;
And a speed control unit that controls the driving speed of the transfer roller driving unit so that the conveyance speed of the recording material follows the rotational speed of the intermediate transfer member based on the output of the detecting unit. An image forming apparatus. The detection means is a rotary encoder that outputs a pulse signal corresponding to a rotation speed of a rotation means for rotating the intermediate transfer member,
The image forming apparatus according to claim 1, wherein the exposure control unit performs exposure control of the exposure unit in synchronization with the pulse signal. The detecting means is a displacement measuring device for detecting a circumferential displacement of a rotating means for rotating the intermediate transfer member,
The image forming apparatus according to claim 1, wherein the speed control unit controls a driving speed of the transfer roller driving unit according to the detected displacement of the peripheral surface.

Images